Mel Giedroyc and Sue Perkins host the semi-final. After seven weeks of gruelling challenges, the four remaining bakers must prove they are worth a place in the final.To begin, the signature challenge requires them to make a baked, layered, mousse cake, and the standards are high as Mary-Anne again attempts something different with a joconde sponge and decor paste.As usual, judges Mary Berry and Paul Hollywood set the tasks. This week's technical challenge is Paul's favourite sweet treat - iced fingers. Finally, for the showstopper, the bakers have to make a labour-intensive and technically demanding layered or laminated pastry dough to produce a batch of three different types of pastries or croissants.With a place in the final within their grasp, the bakers know they have to deliver their very best to the judging table every time.